Final answer:
tRNA is the type of nucleic acid most likely to contain modified bases, as it is involved in protein synthesis with a structure heightened by these modifications. For the purified nucleic acid, if it contains uracil and is bound to amino acids, tRNA is the correct identification.
Step-by-step explanation:
The student question is regarding which type of nucleic acid, among DNA, mRNA, and tRNA, is most likely to contain modified bases. Among the options given, transfer RNA (tRNA) is the type that most commonly contains modified bases. tRNA plays a crucial role in protein synthesis by aligning the correct amino acids with the corresponding mRNA codons, and it has a distinctive structure, including an anticodon loop and an acceptor stem where the amino acid is attached. The presence of modified bases is a characteristic that helps in stabilizing the tRNA structure and in the precise recognition of codons on mRNA.
For the purification question, if the nucleic acid molecules are relatively small, contain uracil, and most are covalently bound to an amino acid, the purified substance is tRNA. DNA does not contain uracil, and mRNA is not typically covalently bound to amino acids. Ribosomal RNA (rRNA) also does not typically bind to amino acids. Hence, tRNA is the correct option.